"""This module contains code from
Think Python by Allen B. Downey

http://thinkpython.com

Copyright 2012 Allen B. Downey
License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html

"""

import os

def walk(dirname):
"""Finds the names of all files in dirname and its subdirectories.

dirname: string name of directory
"""
names = []
for name in os.listdir(dirname):
path = os.path.join(dirname, name)

if os.path.isfile(path):
names.append(path)
else:
names.extend(walk(path))
return names

def compute_checksum(filename):
"""Computes the MD5 checksum of the contents of a file.

filename: string
"""
cmd = 'md5sum ' + filename
return pipe(cmd)

def check_diff(name1, name2):
"""Computes the difference between the contents of two files.

name1, name2: string filenames
"""
cmd = 'diff %s %s' % (name1, name2)
return pipe(cmd)

def pipe(cmd):
"""Runs a command in a subprocess.

cmd: string Unix command

Returns (res, stat), the output of the subprocess and the exit status.
"""
fp = os.popen(cmd)
res = fp.read()
stat = fp.close()
assert stat is None
return res, stat

def compute_checksums(dirname, suffix):
"""Computes checksums for all files with the given suffix.

dirname: string name of directory to search
suffix: string suffix to match

Returns: map from checksum to list of files with that checksum
"""
names = walk(dirname)

d = {}
for name in names:
if name.endswith(suffix):
res, stat = compute_checksum(name)
checksum, _ = res.split()

if checksum in d:
d[checksum].append(name)
else:
d[checksum] = [name]

return d

def check_pairs(names):
"""Checks whether any in a list of files differs from the others.

names: list of string filenames
"""
for name1 in names:
for name2 in names:
if name1 < name2:
res, stat = check_diff(name1, name2)
if res:
return False
return True

def print_duplicates(d):
"""Checks for duplicate files.

Reports any files with the same checksum and checks whether they
are, in fact, identical.

d: map from checksum to list of files with that checksum
"""
for key, names in d.iteritems():
if len(names) > 1:
print 'The following files have the same checksum:'
for name in names:
print name

if check_pairs(names):
print 'And they are identical.'

if __name__ == '__main__':
d = compute_checksums(dirname='.', suffix='.py')
print_duplicates(d)